A fluid is capable of flowing and can easily change its shape. Gases and liquids are fluids. Whether something floats or sinks in a fluid depends on the weight of the substance and the weight of an equal amount the fluid the substance displaces.
- The weight of the egg in this experiment is equal to the force of gravity pulling the egg down.
- The weight of the fluid displaced by the egg is equal to the buoyant force of the fluid pushing up on the egg.
- It is much like a Tug-of-War with forces pulling in opposite directions on the egg.
1. For example, if a fresh raw egg is placed in a container of water, the egg will sink to the bottom of the container. This is because the weight of the egg is greater than the weight of the water the egg displaces (PUSHES ASIDE).
- The winner of the Tug-of-War in this example is gravity. Thus, the egg sinks to the bottom of the glass.
|2. If you dissolve salt in the water, a solution is formed. The more salt that is dissolved in the water, the greater is the weight of the salt solution. Since the weight of the egg remains the same, the egg in this picture rises but stays suspended below the surface of the water. This is because the force of gravity pulling the egg down is equal or almost equal to the buoyant force pushing the egg up. Adding salt to the water only changes the weight of the salt solution; the force of gravity and the weight of the egg remain constant.
3. The egg in this example is floating on the surface of the fluid. Remember that the force of gravity and the weight of the egg remain constant. Thus, the egg rises higher in the salt solution because of the buoyant force has increased. Increasing the buoyant force is achieved by adding more salt, thus making the salt solution heavier.
Can you explain why it is easier to float in the ocean than in a lake? Why is it difficult to sink in the Great Salt Lake in Utah?
For more information about buoyancy, see: